The field of the invention pertains to endoscopes and, in particular, to the position of an endoscope as it is advanced through an orifice in the human body. The position is of particular importance in advancing a colonoscope through the gut because of the convoluted shape of the gut and the danger of damage to the gut wall at locations of steep curvature and loop.
A variety of techniques have been used to visualize the colonoscope as it is advanced in the gut. Perhaps the most obvious technique is fluoroscopy. Unfortunately, fluoroscopy requires expensive, bulky and awkward equipment externally positioned over the patient. Fluoroscope time is generally a scarce resource in even the best equipped medical centers. Most important is the extended time period of x-radiation exposure to the patient, endoscopist and other hospital personnel.
To avoid the use of fluoroscopy other approaches to measuring the position and, in particular, the curvature of the colonoscope as it is advanced through the colon have been proposed. Magnetic field sensors have had some experimental development. In one approach, miniature inductive sensors were placed within the biopsy channel of an endoscope. A magnetic field was created around the exterior of the patient. As the sensors were moved through the biopsy channel an electric signal was generated and the signals monitored by a computer which calculated the path of the sensors as they moved through the biopsy channel. Since the biopsy channel follows through the endoscope, the position and configuration of the endoscope can be generated by the computer to provide a three dimensional image of the endoscope. This magnetic field sensor is disclosed in Bladen, I. S. et al.: "Non-Radiological Technique For Three Dimensional Imaging Of Endoscope", The Lancet, pp. 719-722, Vol. 341: Mar. 20, 1993.
A similar study was done with a magnetic field and coil to generate an image of the endoscope in the colon during motion of a sensor rod. This study was reported in Williams, Christopher, et al.: "Electronic Three-Dimensional Imaging Of Intestinal Endoscope", The Lancet, pp. 724-725, Vol. 341: Mar. 20, 1993.
The magnetic approach has several disadvantages. The first system above requires several low frequency magnetic field generators in order to obtain the signals from the sensor. Thus, the system is expensive and cumbersome with portions that cover the patient's entire abdomen thus interfering with the endoscopic procedure. Moreover, a non-metallic operating platform or bed is required and the patient must not move during the detection period. Similar problems arise with the second system above.
Devices to measure the curvature of pipes without external field devices, whether radiative or magnetic, have been developed for inspecting steam generators in nuclear power facilities. Disclosed in U.S. Pat. No. 4,651,436 is a bendable plug that is moved through a pipe. As the plug moves and bends, sensors communicate the changes in bending of the plug to electrical measurement means for the sensors. In particular, FIG. 5 shows strain gages on the exterior of a flexible tube.
U.S. Pat. No. 4,910,877 shows a similar flexible device adapted to pass through steam generator pipes and provide an electrical signal from a strain gage as the device negotiates bends in the pipes. These devices, however, are relatively large, on the order of inches in diameter, and need only negotiate a few degrees of bend.
More directly related to endoscopes and measurement of the position and posture of the device is U.S. Pat. No. 5,060,632 wherein FIG. 101 shows curvature sensors on the exterior of a bendable portion near the tip of the endoscope. The bent state is monitored electrically as the external controls on the endoscope are manipulated to bend the endoscope during advancement. Thus, the curving path of the head of the endoscope can be monitored as the head advances. Means to cause the head to bend are also shown in U.S. Pat. No. 4,873,965.